All instances of a given area will have the same area layout, for all players. Also, the minimap will automatically be fully revealed.
Multiple Race Events regularly will have the same seed. That is, the instance area layouts will be same in all the races of a fixed seed set.

So the difference is 15 minutes. 15 minutes goes into 105 7 times, and into 90 6 times. Really you will moan that 90minutes should be 24 points and 105minutes should be 31? Your pointless complaints are more illogical.